Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$95.88	13.764%	$109.0769	$109.08	$109.10	$109.10
Purchase #2	$44.61	12.123%	$50.0181	$50.02	$50.00	$50.00
Purchase #3	$140.87	11.359%	$156.8714	$156.87	$156.85	$156.90
Purchase #4	$128.26	9.832%	$140.8705	$140.87	$140.85	$140.90
Purchase #5	$92.78	11.592%	$103.5351	$103.54	$103.55	$103.50
Purchase #6	$205.82	4.644%	$215.3783	$215.38	$215.40	$215.40
Purchase #7	$52.54	11.658%	$58.6651	$58.67	$58.65	$58.70
7 purchase totals =	$760.76		$834.4154	$834.43	$834.40	$834.50